Variable resistor having an improved wiper member

ABSTRACT

A variable resistor of the rotary type is illustrated having a rotatable wiper member, a substrate member carrying an arcuate resistance element and a collector element, all coaxially secured in a cylindrical housing. The wiper member comprises a relatively rigid carriage element having a screw driver slot therein for rotating the wiper member from the exterior of the housing. A resilient pad element is adhesively secured to the carriage element. A flexible contact element is secured to the face of the pad element facing the resistance and collector elements so that the contact element makes electrical contact between the collector and the desired location on the resistance element. The spacing between the substrate member and the carriage member within the housing is less than the uncompressed thickness of the pad element so that the pad urges the contact element into firm engagement with the resistance and collector elements. A portion of the pad element forms a peripheral seal with the substrate member to prevent the passage of contaminates to the resistance element.

United States Patent [191 Hubert [54] VARIABLE RESISTOR HAVING ANIMPROVED WIPER MEMBER [75] Inventor: Gustav Hubert, Gabriel, Calif.

[73] Assignee: Spectrol Electronics Corporation,

City of Industry, Calif.

[ Notice: The portion of the term of this patent subsequent to Mar. 28,1989, has been disclaimed.

[22] Filed: Dec. 14, 1971 [21] Appl. No.: 207,753

Related U.S. Application Data [63] Continuation-in-part of Ser. No.118,750, Feb. 25,

1971, Pat. No. 3,652,970.

[52] U.S. Cl. ..338/174, 338/202 [51] Int. Cl. ..H0lc 1/12 [58] Field ofSearch ..338/160, 162, 164, 167, 114, 338/113, 111, 99, 71, 68, 93,96,118,170,

[56] References Cited UNITED STATES PATENTS 3,652,970 3/1972 Hubert338/183 [451 *Apr. 3, 1973 Primary Examiner-Richard B. WilkinsonAssistant Examiner-U. Weldon Attorney-Harry G. Martin, Jr. et a1.

[57] ABSTRACT A variable resistor of the rotary type is illustratedhaving a rotatable wiper member, a substrate member carrying an arcuateresistance element and a collector element, all coaxially secured in acylindrical housing. The wiper member comprises a relatively rigidcarriage element having a screw driver slot therein for rotating thewiper member from the exterior of the housing. A resilient pad elementis adhesively secured to the carriage element. A flexible contactelement is secured to the face of the pad element facing the resistanceand collector elements so' that the contact element makes electricalcontact between the collector and the desired location on the resistanceelement. The spacing between the substrate member and the carriagemember within the housing is less than the uncompressed thickness of thepad element so that the pad urges the contact element into firmengagement with the resistance and collector elements. A portion of thepad, element forms a peripheral seal with the substrate member toprevent the passage of contaminates to the resistance element.

- 3 Claims, 4 Drawing Figures 2O \\l 3 INVENTOR.

GUSTAV HUBERT 5O FIIG.4 "M

ATTORNEY VARIABLE RESISTOR HAVING AN IMPROVED WIPER MEMBER CROSSREFERENCE TO RELATED APPLICATION Features of this invention aredisclosed in my copending application, Ser. No. 118,750, filed Feb. 25,

BACKGROUND OF THE INVENTION This invention relates to variable resistorsand more particularly to improved wiper elements suitable for rotarypotentiometers.

Variable resistors, especially of the miniature, rotary trimmingpotentiometer type, have found wide acceptance because of their smallsize and low cost. Often they are used in an adverse environmentallocation where it is necessary to restrict the entrance of ambient gasesor liquids into the interior of the potentiometer to prevent failurethereof. Also, the potentiometer may have to be sealed in the event itis to be installed on a printed circuit board which is washed with asolvent during the manufacturing process. In any event, it is highlydesirable to prevent the entrance of moisture, dirt, abrasive matter andcorrosive chemicals into the region occupied by the resistance and wiperelements toavoid failures or excessive electrical noise due to contactresistance variation and to prevent mechanical damage to the resistanceelement and the wiper contact by abrasion.

While conventional sealing arrangements, such as rings, often providesatisfactory seals, the small size sealing rings required in miniaturepotentiometers requires a tedious hand assembly operation which addsexcessive cost to the unit in the event of good seal is not required fora particular application. Furthermore, prior sealing designs provide anair space within the potentiometer which, due to temperature or pressurevariations to which it issubjected in manufacture or use, can give riseto a sufficient pressure difference across the seal to result in passageof ambient foreign material past the seal into the interior of the unitand eventually degrade or impair its operation.

Accordingly, it is a principal feature of this invention to provide arelatively simple trimmer potentiometer design having an effective,easily assembled and inexpensive sealing means to prevent the entranceof foreign material into the region of the resistance element and wiperelement.

SUMMARY OF THE INVENTION An insulating substrate member is provided withan elongated resistance element and collector element thereon. A movablewiper member is provided with means for adjusting its movement. Thewiper member comprises a relatively rigid carriage element having arelatively resilient pad element secured thereto. A wiper contactelement is secured to the face of the pad element which faces theresistance and collector elements. The substrate member and the carriageelement are secured so that the distance therebetween is less than thenormal uncompressed thickness of the pad element so that the pad elementurges the wiper contact into firm electrical engagement with theresistance element and the collector element. The pad element overliesthe resistance element and forms a peripheral seal with the substratewhich resists contamination of the resistor and collector elements withforeign material.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a central cross-sectionalview through a variable resistor in accordance with this invention;

FIG. 2 is an isometric view of improved wiper member in accordance withthis invention;

FIG. 3 is an isometric view of the substrate member showing theresistance and collector elements thereon; and

FIG. 4 is a cross-sectional view taken substantially on line IVIV ofFIG. 1.

DESCRIPTION OF A PREFERRED EMBODIMENT Referring to the drawings, thereis shown a variable resistor 10 which in the preferred embodiment may bea trimmer potentiometer. Variable resistor 10 is provided with a housingmember 1 1 having a hollow, cylindrical interior cavity which ispreferably circular in cross-section. A rotatable wiper member 12 and asubstrate member 13, which are also preferably circular incross-section, are coaxially disposed within the circular cavity in thehousing 1]. Terminal members 14, 15 and 16 are provided for makingelectrical connections with the resistance element.

One face 19 of substrate 13 is providedwith an elongated arcuateresistance element 20 having its ends deposited over and electricallycontacting suitable conductive terminations 21, 22. Resistance element20 is preferably of the cermet type which comprises a plurality of metalor metallic alloy particles dispersed throughout a ceramic glass coatingwhich may be deposited on face 19 of substrate member 13 by screenprinting and subsequent firing. Substrate member 13 is preferablycomposed of a ceramic insulating material such as alumina. Conductiveterminations 21, 22 may also be deposited on face 19 of substrate 13 byscreen printing and comprise a highly conductive metallic coating.Terminal members 15 and 16 are inserted through appropriate holes insubstrate 13 and soldered or brazed to make electrical contact withterminations 21 and 22 which form the electrical ends of resistanceelement 20.

A suitable collector element 25 is formed in the center of substrate 13.Collector element 25 may comprise a conductive metal coating 26, similarto terminations 21 and 22, formed around a central hole 27 throughsubstrate 13. Terminal member 14 is bent to a desired shape to providethe desired final terminal pin configuration and one end thereofinserted through the hole formed by conductive coating 26. Solder orother conductive brazing material 25 is then applied to electrically andmechanically secure terminal 14 to conductive coating 26 and at the sameto form a conductive surface region about the central area of substrate13 as shown in the drawings. Alternatively, collector element 25 may beformed by depositing or securing a suitable conductive coating orelement into surface 19 of substrate 13 to provide any desired shape forthe collector element. Similarly, the resistance element may be, of anydesired type such as a conductive resin or solid metal resistancematerial and may be arcuate or linear in shape if desired, and may besecured by any desired means to substrate 13.

Wiper member 12 is cylindrical in the embodiment illustrated, and ismounted coaxially within interior cavity 17 of housing 11. Wiper member12 comprises a relatively rigid carriage element 30 which is provided Iwith means for adjusting its position from the exterior of housing 11.In the embodiment shown, carriage element 30 has a cylindrical, axialprojection 31 which extends through a correspondingly shaped aperture inhousing to allow rotational adjustment of the carriage element from theexterior of the housing by insertion of screw driver in screw driverslot 32. Alternatively, the carriage element may be provided with gearteeth so that it can be rotated by worm screw projecting externally fromthe housing.

Carriage element has one face 33 which faces toward substrate member 13when the members are inserted in the housing. The other face 34 extendsradially outwardly from cylindrical projection 31 and abuts against anopposing annular shoulder 35 on housing 1 1. If desired, an O-ring orother seal means (not shown) may be provided between shoulders 34 and 35to resist the entrance of dirt, moisture or other contaminates into theinterior of housing 11.

Wiper member 12 also comprises a pad element which is made of aresilient material such as silicone rubber. Pad element 40 may be madeof various resilient materials such as felt, poly-urethane foam orneoprene.- Preferably, the material selected for pad 40 is relativelyimpervious to moisture and is capable of withstanding whatever heat thevariable resistor may be subjected to without losing resiliency.Resilient pad 40 is circular in cross-section and'is coaxially mountedwithin the interior of housing 11 with one surface 41 thereof facingsubstrate member 13. The other surface 42 of pad 40 is secured tocarriage element 30 by adhesive 43, such as an epoxy glue, or othersuitable means such as molding. v

A conductive wiper contact element 45 is disposed on one surface 41 ofpad element Wiper contact element 45 preferably comprises a relativelydeformable bar of finely divided electrically conducting metal particleswhich are flexibly bonded together by a suitable material such as aflexible or deformable resinous plastic binder. Contactelement 45 maycomprise a flexible epoxy plastic filled with finely divided silverparticles. Alternatively, wiper contact element 45 may comprise anyelectrical conductor such as metallic ink, flexible foil, wire woolorone or more metal wires disposed on face 41 of 'pad element 40. Wipercontact I element 45 is preferably sufficiently deformable or flexible,thick and electrically conductive sothat the contact element can followthe resilient deformation of pad 40 and makegood electrical contactbetween the resistance and collector elements. The wiper contact elementis disposed in spaced relation with the edge of pad 40 so that aneffective seal is formed radially outwardly of the wiper contactelement. A silver filled epoxy plastic bar having a thickness of about0.04 inches and a width of 0.05 inches has been found to produce verygood electrical characteristics.

Substrate member 13 is coaxially secured in housing 11 by any desiredmeans. It is preferred to secure substrate 13 in housing 11 by use of aninsulating epoxy potting agent 50. Substrate member 13 is secured withinthe housing 1 1 so that the distance between face 33 of carriage element30 and the upper surfaces of resistance element 20, collector element25and face 19 of substrate member 13 is less than the uncompressed axialthickness of resilient pad element 40. Consequently, pad element 40axially urges wiper contact element 45 into firm electrical andmechanical'engagement with resistance element 30 and collector elementit is preferred to assemble the elements and members within housing 11and to apply an axial force of about one pound on substrate member 13 bya suitable device to initially compress resilient pad element 40. As asmall amount of the epoxy potting agent 50 is then poured into cavity 17and cured sufficiently to secure substrate 13 in the desired position tohold pad 40. com-.

pressed. Thereafter the device exerting pressure on substrate 13 isremoved and additional epoxy agent is poured into cavity 17 and finallycured to complete the assembly.

Pad element 40 extends radially outward from the axis of wiper member12, an extent greater than resistance element 20 and wiper contactelement 45 so that it completely overlies the resistanceand wiperelements. Consequently, an effective seal is formed adjacent theperipheral edges of pad element 40 and substrate member 13 at a locationradially outwardly of the resistor and collector elements to effectivelyresist the entrance of foreign material between them. The sealcompletely surrounds both the resistor and collector elements to resistthe passage of foreign material to them. The seal is also formedradially outwardly of the wiper contact element so" that passage offoreign material to the wiper contact element is resisted. A suitablelubricant, such as petroleum grease having a lithium anti-frictioncompound therein maybe provided between pad element 40,and substratemember 13. The lubricant not only serves the function of improving thesetability of the wiper member by reducing its friction withthesubstrate, resistance and collector elements, but in addition, itserves to coat the surface of any foreign particles with a dielectricfilm to reduce noise.

It will be seen that a construction in accordance with this inventionpossesses the advantage of being simple and inexpensive to manufactureand easy to assembly in either a manual or automated production process.

The resilient pad serves to bias the wiper contact into engagement withthe resistor and collector tracks and to form an effective sealingmeans, thereby eliminating the necessity of a separate seal and theattendant cost of assembling a separate seal. Further, there is no airspace on the resistor side of the seal to create a pressure differenceunder varying temperature conditions.

While for purposes of illustration a preferred embodiment of thisinvention has been described, it will be apparent that the invention maybe otherwise embodied within the scope of the following claims.

I claim:

1. A variable resistor comprising:

A. a substrate member comprising an electrically insulating material,one face of said substrate member being substantially flat, an arcuateresistance element disposed on said one face of said substrate member,and a collector element disposed on said one face of said substratemember;

B. a wiper member comprising:

C. a rotatable wiper member, said wiper member 1. arelatively rigidcarriage element; 5 being disposed for rotation within said housing 2. arelatively resilient, pad element secured to member and having meansassociated therewith said carriage element in overlying relation withfor adjusting the rotational position of said wiper the entire extent ofsaid resistance element and member from the exterior of said housingmember, said collector element; said wiper member comprising:

3. a wiper contact element disposed on said pad 10 l. a relatively rigidcarriage element disposed for element, said contact element comprisingan rotation in the cavity in said housing member; electricallyconductive element overlying and 2. a relatively resilient, pad elementsecured to said contacting portions of both said resistance elecarriageelement, said pad element having one ment and said collector element;substantially flat face compressed against said one 4. means forrotating said wiper member relative l5 face of said substrate member,said pad element to said substrate member so that the wiper conoverlyingthe entire extent of said resistance eletact can be moved across thearcuate resistance ment and said collector element to sealinglyenelement to adesired location thereon; gage said one face of saidsubstrate member at a 5. said carriage element being spaced from saidrelocation radially outward of said resistor and colsistance andcollector elements by a fixed 2O lector elements to resist the passageof foreign distance less than the uncompressed thickness material tosaid resistance and collectorelements; of said resilient pad element sothat said resilient a "P Contact n olsposed on Sald one o pad element iscompressed to resiliently use of said pad element, sa d contact elementcompris- Said Contact element into firm electrical and mg a radiallyextending electrically conductive mechanical engagement with saidresistor and Contact o f overlymg and oontactlng pornons collectorelements, Said pad element being of both said resistance element andsaid collector pressed against and sealingly engaging the element, saidpad element extending radially outstrate member at a location radiallyoutwardly woroly beyond the n element; of and completely Surrounding thecollector 4. sa d carriage element and said substrate member ment andthe arcuate resistance element to rebemg spaced apart nouslng by aolstanoe sist the passage of contaminants to the resistor than theuncompressed of Sam and collector elements; and resilient pad element sothat said resilient pad ele- C. terminal means for making electricalcontact with ment P o between 5am suosn'ate said collector element andsaid resistance element. member 3 531d ge e ement to urge said one 2. Avariable resistor as defined in claim 1 wherein o Said pad elementSeanng engagement said resilient pad element extends radially outwardlyn one face of solo suostrate menfber at a beyond Said wiper Contactelement cation completely surrounding the resistance ele- A variableresistor comprising; ment, the collector element and the wiper contactA. a housing member, said housing member having n and to urge SoloContact element P animerior cavity therein; 40 electrical and mechanicalengagement with said B. a substrate member comprising an electricallyinreslstor and collector elefnonts; n

Sulating material one face of Said substrate D. terminal means formaking electrical contact with member being Substantially flat andfacing the said collector element and sa d resistance element teriorcavity of said housing member, an arcuately from the extenor of soldnouslng member' extending resistance element disposed on said one

1. A variable resistor comprising: A. a substrate member comprising anelectrically insulating material, one face of said substrate memberbeing substantially flat, an arcuate resistance element disposed on saidone face of said substrate member, and a collector element disposed onsaid one face of said substrate member; B. a wiper member comprising: 1.a relatively rigid carriage element;
 2. a relatively resilient, padelement secured to said carriage element in overlying relation with theentire extent of said resistance element and said collector element; 3.a wiper contact element disposed on said pad element, said contactelement comprising an electrically conductive element overlying andcontacting portions of both said resistance element and said collectorelement;
 4. means for rotating said wiper member relative to saidsubstrate member so that the wiper contact can be moved across thearcuate resistance element to a desired location thereon;
 5. saidcarriage element being spaced from said resistance and collectorelements by a fixed distance less than the uncompressed thickness ofsaid resilient pad element so that said resilient pad element iscompressed to resiliently urge said contact element into firm electricaland mechanical engagement with said resistor and collector elements,said pad element being compressed against and sealingly engaging thesubstrate member at a location radially outwardly of and completelysurrounding the collector element and the arcuate resistance element toresist the passage of contaminants to the resistor and collectorelements; and C. terminal means fOr making electrical contact with saidcollector element and said resistance element.
 2. a relativelyresilient, pad element secured to said carriage element in overlyingrelation with the entire extent of said resistance element and saidcollector element;
 2. A variable resistor as defined in claim 1 whereinsaid resilient pad element extends radially outwardly beyond said wipercontact element.
 2. a relatively resilient, pad element secured to saidcarriage element, said pad element having one substantially flat facecompressed against said one face of said substrate member, said padelement overlying the entire extent of said resistance element and saidcollector element to sealingly engage said one face of said substratemember at a location radially outward of said resistor and collectorelements to resist the passage of foreign material to said resistanceand collector elements;
 3. a wiper contact element disposed on said oneface of said pad element, said contact element comprising a radiallyextending electrically conductive contact element overlying andcontacting portions of both said resistance element and said collectorelement, said pad element extending radially outwardly beyond the wipercontact element;
 3. A variable resistor comprising: A. a housing member,said housing member having an interior cavity therein; B. a substratemember comprising an electrically insulating material, one face of saidsubstrate member being substantially flat and facing the interior cavityof said housing member, an arcuately extending resistance elementdisposed on said one face of said substrate member, and a collectorelement disposed on said one face of said substrate member; C. arotatable wiper member, said wiper member being disposed for rotationwithin said housing member and having means associated therewith foradjusting the rotational position of said wiper member from the exteriorof said housing member, said wiper member comprising:
 3. a wiper contactelement disposed on said pad element, said contact element comprising anelectrically conductive element overlying and contacting portions ofboth said resistance element and said collector element;
 4. means forrotating said wiper member relative to said substrate member so that thewiper contact can be moved across the arcuate resistance element to adesired location thereon;
 4. said carriage element and said substratemember being spaced apart in said housing by a distance less than theuncompressed thickness of said resilient pad element so that saidresilient pad element is compressed between said substrate member andsaid carriage element to urge said one face of said pad element intosealing engagement with said one face of said substrate member at alocation completely surrounding the resistance element, the collectorelement and the wiper contact element, and to urge said contact elementinto electrical and mechanical engagement with said resistor andcollector elements; and D. terminal means for making electrical contactwith said collector element and said resistance element from theexterior of said housing member.
 5. said carriage element being spacedfrom said resistance and collector elements by a fixed distance lessthan the uncompressed thickness of said resilient pad element so thatsaid resilient pad element is compressed to resiliently urge saidcontact element into firm electrical and mechanical engagement with saidresistor and collector elements, said pad element being compressedagainst and sealingly engaging the substrate member at a locationradially outwardly of and completely surrounding the collector elementand the arcuate resistance element to resist the passage of contaminantsto the resistor and collector elements; and C. terminal means fOr makingelectrical contact with said collector element and said resistanceelement.